As is well known in the art, when a spun yarn of synthetic material, such as polyester, polyamide and polyacrylic, is manufactured, a tow, consisting of a plurality of multifilaments, is subjected to a predetermined treatment, such as a drawing process and a crimping process, and then, is cut into staple fibers having a predetermined length by a cutting knife or cutting knives of a cutting apparatus. Then, after the staple fibers are sent to a spinning process where they are made into a bundle, such as a fleece and a sliver, a yarn is spun from the bundle.
However, the above-mentioned method, in which a tow is cut into staple fibers and then a yarn is spun from the staple fibers has a very low efficiency because the multifilaments which are parallel to each other in the tow are placed in disorder when they are cut into staple fibers, and because the staple fibers are paralleled again in the spinning process.
To obviate the above-mentioned problem of low efficiency, converting methods have been proposed in which a tow consisting of parallel multifilaments is directly converted into a sliver without causing a degradation of the parallel condition of the multifilaments. One of the converting methods is a stretch breaking method in which a tow is stretched with a large draft ratio and, then, multifilaments composing the tow are broken into staple fibers. When a spinning process is added after the above-mentioned stretch breaking process, an economical method for manufacturing a spun yarn can be obtained, in which a tow is directly converted into a spun yarn.
Known in the art is an apparatus for effecting the above-mentioned stretch breaking method. That apparatus comprises: a pair of feed rollers for holding and supplying multifilament bundle; a pair of draft rollers, having a higher peripheral speed than that of the feed rollers, for stretch breaking the multifilaments of the tow between the feed rollers and the draft rollers; and an apron belt, belted at a space between the feed rollers and the draft rollers, for transfering the bundle to the draft rollers.
In addition to the above-mentioned stretch breaking apparatus, a rotating fluid torque jet device is disclosed in the U.S. Pat. No. 3,079,746, issued to Field, on Mar. 5, 1963. By utilizing this apparatus it is possible to carry out a direct spinning process in which a tow consisting of multifilaments is directly converted into a spun yarn after stretch breaking.
However, when a multifilament bundle of a synthetic material is treated by the above-mentioned stretch breaking process disclosed by Field, the uniformity in the quality of the sliver and that of the spun yarn manufactured from the sliver are decreased as the stretch breaking speed is increased, and a problem of unevenness of the sliver thickness and the spun yarn occurs. The problem of unevenness is apparent when the stretch breaking speed is not less than 200 m/min and is very troublesome when the stretch breaking speed is not less than 300 m/min.
To obviate the problem of the unevenness, a method is proposed in the Japanese laid-open patent application No. 119851/76 (corresponding U.S. patent application Ser. No. 56427), applicant E. I. du Pont de Nemours and Company. In this method, continuous multifilaments of synthetic material having a maximum elongation of not more than 70% are supplied to a draft zone. In the draft zone, the multifilaments are free from any support and are subjected to stretch breaking by using a draft ratio of from 5 to 100 between the input rollers and delivery rollers, both of which are vertically juxtaposed, the distance between the rollers being between 65 and 130 cm, without causing the storage of static electricity on the multifilaments. Thus discontinuous fibers having several average fiber lengths between 18 and 60 cm are created. After stretch breaking, the fibers are taken up from the draft zone by passing them onto a perforated draft roller which is provided with a sucking jet formed thereon, and are entangled so as to spin them into a yarn.
However, in the above described method, broken filaments held by the delivery rollers, especially broken filaments at a peripheral portion of the bundle, may easily hang down due to the dead load of the filament, because the filaments are free from the support in the draft zone. In addition, broken ends of filaments held by the input rollers may become hook-shaped due to the spring-back of the filaments at the moment when they are subjected to stretch breaking. As a result, ends of filaments may be entangled around the delivery rollers, and the entanglement of the filaments decreases the evenness of the sliver.